U.S. patent number 6,579,018 [Application Number 09/465,066] was granted by the patent office on 2003-06-17 for four-fiber ring optical cross connect system using 4.times.4 switch matrices.
This patent grant is currently assigned to Corning Incorporated. Invention is credited to Ming-jun Li, Mark J. Soulliere.
United States Patent |
6,579,018 |
Li , et al. |
June 17, 2003 |
Four-fiber ring optical cross connect system using 4.times.4 switch
matrices
Abstract
An optical cross-connect system provides 4.times.4 switching
matrices and self-healing from any single point of failure. The
switching matrices route working traffic and redundant protection
traffic between a plurality of client network elements and an
optical ring. The system also has a client interface for
transporting the working traffic and the protection traffic between
the switching matrices and the client network elements. The optical
cross-connect system further includes a ring interface for
transporting the working traffic and the protection traffic between
the switching matrices and the optical ring. The switching matrices
are structured so that protection is provided from single point
failures by electrical switching at the client network element
location. This significantly reduces the need for optical switching
within the matrices.
Inventors: |
Li; Ming-jun (Horse Heads,
NY), Soulliere; Mark J. (Corning, NY) |
Assignee: |
Corning Incorporated (Corning,
NY)
|
Family
ID: |
23846364 |
Appl.
No.: |
09/465,066 |
Filed: |
December 16, 1999 |
Current U.S.
Class: |
398/4; 398/49;
398/7; 398/83 |
Current CPC
Class: |
H04J
14/0212 (20130101); H04J 14/0217 (20130101); H04J
14/0283 (20130101); H04J 14/0291 (20130101); H04J
14/0294 (20130101); H04J 14/0297 (20130101); H04Q
11/0062 (20130101); H04Q 2011/0024 (20130101); H04Q
2011/0081 (20130101); H04Q 2011/0092 (20130101) |
Current International
Class: |
H04Q
11/00 (20060101); H04J 14/02 (20060101); H04B
010/08 () |
Field of
Search: |
;398/4,49,7,83
;385/16,17,18,19,24,37 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Elrefaie, A.F.; "Multiwavelength Survivable Ring Network
Architectures"; IEEE, May 23-26, 1993. .
Fujimoto et al; "Broadband Subscriber Loop System Using
Multi-Gigabit Intelligent Optical Shuttle Nodes"; IEEE Nov. 15-18,
1987..
|
Primary Examiner: Pascal; Leslie
Assistant Examiner: Phan; Hanh
Attorney, Agent or Firm: Bean; Gregory V.
Claims
What is claimed is:
1. An optical cross-connect system for use with work traffic and
protection traffic for a plurality of clients and an optical ring,
the optical cross-connect system comprising: a pair of 4.times.4
optical switching matrices for routing the working traffic and the
protection traffic between the plurality of clients and the optical
ring; a client interface for transporting the working traffic and
the protection traffic between the pair of 4.times.4 optical
switching matrices and the plurality of clients; and a ring
interface for transporting the working traffic and the protection
traffic between the pair of 4.times.4 optical switching matrices
and the optical ring wherein the plurality of clients includes a
first client and a second client, and further wherein the pair of
4.times.4 optical switching matrices comprises: a first matrix, the
first matrix adding the traffic from the second client to the
optical ring, adding the protection traffic from the first client
to the optical ring, dropping the working traffic from the optical
ring to the first client, and dropping the protection traffic from
the optical ring to the second client; and a second matrix, the
second matrix adding the working traffic from the first client to
the optical ring, adding the protection traffic from the second
client to the optical ring, dropping the working traffic from the
optical ring to the second client, and dropping the protection
traffic from the optical ring to the first client.
2. The optical cross-connect system of claim 1 wherein each of the
plurality of client network elements has an electrical bridge and a
protection switch, the electrical bridge adding the working traffic
and the protection traffic to the client network element interface,
and the protection switch selecting the working traffic as an
incoming signal.
3. The optical cross-connect system of claim 2 including a working
span wherein a single point failure occurs in the working span and
affects an affected local client network element, and as a result
the protection switch of the affected local client network element
selects the protection traffic as an incoming signal, and wherein
the pair of 4.times.4 optical switching matrices do not change.
4. The optical cross-connect system of claim 3 including add drop
nodes with working fibers therebetween in the optical ring, wherein
the single point failure occurs in the working fibers between the
add drop nodes of the optical ring.
5. The optical cross-connect system of claim 3 wherein the single
point failure occurs in the ring interface.
6. The optical cross-connect system of claim 3 wherein the single
point failure occurs in one of the pair of 4.times.4 optical
switching matrices.
7. The optical cross-connect system of claim 3 wherein the single
point failure occurs in the client network element interface.
8. An optical cross-connect system for use with work traffic and
protection traffic for a plurality of clients and an optical ring,
the optical cross-connect system comprising: a pair of 4.times.4
optical switching matrices for routing the working traffic and the
protection traffic between the plurality of clients and the optical
ring; a client interface for transporting the working traffic and
the protection traffic between the pair of 4.times.4 optical
switching matrices and the plurality of clients; and a ring
interface for transporting the working traffic and the protection
traffic between the pair of 4.times.4 optical switching matrices
and the optical wherein the plurality of clients includes a first
client and a second client, and further wherein there is an
adjacent cable and a single point failure occurs as an adjacent
cable cut, the pair of 4.times.4 switching matrices comprising: a
first matrix, the first matrix adding the working traffic from the
second client to the optical ring, and dropping the protection
traffic from the optical ring to the first client as the working
traffic; and a second matrix, the second matrix adding the working
traffic from the first client to the optical ring as the protection
traffic, and dropping the working traffic from the optical ring to
the second client.
9. An optical cross-connect system for use with work traffic and
protection traffic for a plurality of clients and an optical ring,
the optical cross-connect system comprising: a pair of 4.times.4
optical switching matrices for routing the working traffic and the
protection traffic between the plurality of clients and the optical
ring; a client interface for transporting the working traffic and
the protection traffic between the pair of 4.times.4 optical
switching matrices and the plurality of clients; and a ring
interface for transporting the working traffic and the protection
traffic between the pair of 4.times.4 optical switching matrices
and the optical ring wherein the plurality of clients includes a
first client and a second client, the optical cross-connect system
include an adjacent cable and nodes, and wherein a single point
failure occurs as a non-adjacent cable cut and nodes adjacent to
the single point failure reverse the working traffic with the
protection traffic, the pair of 4.times.4 switching matrices
comprising: a first matrix, the first matrix adding the working
traffic from the second client to the optical ring, passing the
protection traffic through, and dropping the working traffic from
the optical ring to the first client; and a second matrix, the
second matrix adding the working traffic from the first client to
the optical ring, passing the protection traffic through, and
dropping the working traffic from the optical ring to the second
client.
10. An optical cross-connect system for use with work traffic and
protection traffic for a plurality of clients and an optical ring,
the optical cross-connect system comprising: a pair of 4.times.4
optical switching matrices for routing the working traffic and the
protection traffic between the plurality of clients and the optical
ring; a client interface for transporting the working traffic and
the protection traffic between the pair of 4.times.4 optical
switching matrices and the plurality of clients; and a ring
interface for transporting the working traffic and the protection
traffic between the pair of 4.times.4 optical switching matrices
and the optical ring including an adjacent cable and nodes wherein
a single point failure occurs as a non-adjacent cable cut and the
nodes do not change, the pair of 4.times.4 switching matrices
comprising: a first matrix, the first matrix adding the working
traffic from the second client to the optical ring as protection
traffic, dropping the working traffic from the optical ring to the
first client, and dropping the protection traffic from the optical
ring to the second client; and a second matrix, the second matrix
adding the working traffic from the first client to the optical
ring, adding the protection traffic from the second client to the
optical ring, and dropping the protection traffic from the optical
ring to the second client as the working traffic.
11. A bi-directional optical ring for use with working traffic and
protection traffic and a plurality of clients, the bi-directional
optical ring comprising: a plurality of optical cross-connect
systems, each of the plurality of optical cross-connect systems
having a plurality of 4.times.4 optical switching matrices for
routing the working traffic and the protection traffic between the
plurality of clients and the optical ring; a plurality of working
spans, each of the plurality of working spans carrying the working
traffic between adjacent ones of the plurality of optical
cross-connect systems; and a plurality of protection spans, each of
the plurality of protection spans carrying the protection traffic
between adjacent ones of the optical cross-connect systems wherein
each of the plurality of 4.times.4 optical switching matrices
comprises: a pair of first matrices, the pair of first matrices
routing the working traffic between the plurality of clients and
the optical ring at a first wavelength; and a pair of second
matrices, the pair of second matrices routing the protection
traffic between the plurality of clients and the optical ring at a
second wavelength.
12. A bi-directional optical ring for use with working traffic and
protection traffic and a plurality of clients, the bi-directional
optical ring comprising: a plurality of optical cross-connect
systems, each of the plurality of optical cross-connect systems
having a plurality of 4.times.4 optical switching matrices for
routing the working traffic and the protection traffic between the
plurality of clients and the optical ring; a plurality of working
spans, each of the plurality of working spans carrying the working
traffic between adjacent ones of the plurality of optical
cross-connect systems; and a plurality of protection spans, each of
the plurality of protection spans carrying the protection traffic
between adjacent ones of the optical cross-connect systems wherein
each of the plurality of 4.times.4 optical switching matrices
comprises: a pair of first matrices, the pair of first matrices
adding the working traffic and the protection traffic from the
plurality of clients to the optical ring at a first wavelength; and
a pair of second matrices, the pair of second matrices dropping the
working traffic and the protection traffic from the optical ring to
the plurality of clients at a second wavelength.
13. A bi-directional optical ring for use with working traffic and
protection traffic and a plurality of clients, the bi-directional
optical ring comprising: a plurality of optical cross-connect
systems, each of the plurality of optical cross-connect systems
having a plurality of 4.times.4 optical switching matrices for
routing the working traffic and the protection traffic between the
plurality of clients and the optical ring; a plurality of working
spans, each of the plurality of working spans carrying the working
traffic between adjacent ones of the plurality of optical
cross-connect systems; and a plurality of protection spans, each of
the plurality of protection spans carrying the protection traffic
between adjacent ones of the optical cross-connect systems wherein
each of the plurality of 4.times.4 optical switching matrices
comprises: a pair of first matrices, the pair of first matrices
adding the working traffic from the plurality of clients to the
optical ring, and dropping the protection traffic from the optical
ring to the plurality of clients at a first wavelength; and a pair
of second matrices, the pair of second matrices adding the
protection traffic from the plurality of clients to the optical
ring, and dropping the working traffic from the optical ring to the
plurality of clients at a second wavelength.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical protection
switching architectures. More particularly, the present invention
is directed to an optical cross-connect system utilizing 4.times.4
switching matrices for providing self-healing from any single point
of failure.
2. Technical Background
In the rapid development of optical communication systems,
networking architectures have become increasingly complex. Ring
topologies have arisen to provide a number of networking elements
with the ability to both listen and transmit on optical channels
within the optical ring. In such a ring topology, consecutive nodes
are connected by point-to-point links which are arranged to form a
single closed path or ring. Information is transmitted from node to
node around the ring, and the interface at each node is an active
device that has the ability to create and accept messages. The
interface serves not only as a user attachment point but also as an
active repeater for re-transmitting messages that are addressed to
other nodes.
A number of implementation considerations must be taken into
account when configuring a ring network. First, rings must be
physically arranged so that all nodes are fully connected. Whenever
a node is added to support new devices, transmission lines have to
be placed between this node and its two nearby, topologically
adjacent nodes. A break in any line, the failure of a node, or
adding a new node threatens to disrupt network operation. A variety
of steps can be taken to circumvent these problems, although this
generally increases the complexity of the ring interface
electronics as well as the associated costs.
The American National Standards Institute (ANSI) has released a
collection of standards for synchronous optical networks (SONET's)
to address a growing bandwidth problem in the wide area network
(WAN) environment. These standards provide signaling protocols for
various types of optical networks but fail to address optical
cross-connect systems with any specificity. Another problem with
structuring a bidirectional optical ring around SONET standards, is
the possibility of transmitting data which is not SONET based. For
example, gigabyte Ethernet signals transmitted to digital clients
often do not fall within SONET standards. Thus, it is desirable to
provide a bidirectional optical ring architecture with the
flexibility of operating within or out of SONET protocols. It is
also desirable to provide improved protection against single point
failures and network changes.
SUMMARY OF THE INVENTION
The above and other objects are provided by an optical
cross-connect system having a pair of 4.times.4 optical switching
matrices. The switching matrices route working traffic and
redundant protection traffic between a plurality of clients and an
optical ring. The optical cross-connect system also has a client
interface for transporting the working traffic and the protection
traffic between the switching matrices and the clients. The optical
cross-connect system further includes a ring interface for
transporting the working traffic and the protection traffic between
the switching matrices and the optical ring. The switching matrices
are structured so that protection is provided from single point
failures by electrical switching at the client location. This
significantly reduces the need for optical switching within the
switching matrices. The 4.times.4 architecture of the matrices
provides a fundamental building block which allows ultimate
flexibility in design of optical rings.
It is to be understood that both the foregoing general description
and the following detailed description are merely exemplary of the
invention, and are intended to provide an overview or framework for
understanding the nature and character of the invention as it is
claimed. The accompanying drawings are included to provide a
further understanding of the invention, and are incorporated in and
constitute part of this specification. The drawings illustrate
various features and embodiments of the invention, and together
with the description serve to explain the principles and operation
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The various advantages of the present invention will become
apparent to one skilled in the art by reading the following
specification and appended claims, and by referencing the following
drawings in which:
FIG. 1 is a schematic illustration of a bidirectional optical ring
implementing the presently preferred cross-connect system;
FIG. 2 is a more detailed view of node B of FIG. 1;
FIG. 3 is a more detailed view of the first client network element
of FIGS. 1 and 2;
FIG. 4 is a schematic illustration of a single point failure of a
working span between add drop nodes;
FIG. 5 is a more detailed view of node B of FIG. 4;
FIG. 6 is a detailed view of an optical cross-connect system with a
single point failure of a demultiplexer;
FIG. 7 is a detailed view of an optical cross-connect system with a
single point failure of a 4.times.4 switching matrix;
FIG. 8 is a detailed view of an optical cross-connect system with a
single point failure of a working span in a client interface;
FIG. 9 is a schematic illustration of a bidirectional optical ring
with a single point failure of a working span which is non-adjacent
to a add drop node;
FIG. 10 is a more detailed view of node B of FIG. 9;
FIG. 11 is a more detailed view of node D of FIG. 9;
FIG. 12 is a detailed view of a through node with a single point
failure of a demultiplexer;
FIG. 13 is a detailed view of a through node with a single point
failure of a 4.times.4 switching matrix;
FIG. 14 is a schematic illustration of a bidirectional optical ring
with a single point failure occurring as a cable cut between add
drop nodes;
FIG. 15 is a more detailed view of node B of FIG. 14;
FIG. 16 is a more detailed view of node D of FIG. 14;
FIG. 17 is a schematic illustration of a bidirectional optical ring
with a single point failure of a cable cut between through
nodes;
FIG. 18 is a more detailed view of node B of FIG. 17;
FIG. 19 is a more detailed view of node D in FIG. 17;
FIG. 20 is an alternative schematic illustration of a single point
failure as a cable cut between through nodes;
FIG. 21 is a more detailed view of node B of FIG. 20;
FIG. 22 is a more detailed view of node D of FIG. 20;
FIG. 23 is a second embodiment of an optical cross-connect system
in accordance with the principals of the invention;
FIG. 24 is a third embodiment of an optical cross-connect system in
accordance with the principals of the present invention;
FIG. 25 is a fourth embodiment of an optical cross-connect system
in accordance with the principals of the present invention;
FIG. 26 is a logic table representing the structure of a first
switching matrix in accordance with the preferred embodiment;
and
FIG. 27 is a logic table of the structure of a second switching
matrix in accordance with the preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Wherever possible, the same reference
numerals will be used throughout the drawings to refer to the same
or like parts.
Referring to FIG. 1, a four-fiber bi-directional optical
communication ring implementing the presently preferred optical
cross-connect system is illustrated at 10. The optical ring is made
up of a plurality of nodes, working spans 100, and protection spans
200. The working spans 100 and protection spans 200 are preferably
implemented via fiber optic waveguide communication channels. Each
node has an optical cross-connect system (OCCS) and one or more
network elements shown as client network elements 1 through 4. A
node can be either an add drop node, such as Nodes A and B, or a
through node, such as Nodes C and D. Essentially, add drop nodes
connect to network elements, whereas through nodes do not connect
to client network elements. Under normal conditions, working spans
100 run between nodes and carry working traffic. Similarly,
protection spans 200 run between nodes and carry redundant
protection traffic.
Referring to FIG. 2, the preferred embodiment for the OCCS at Node
B is shown generally at 20. OCCS 20 has a pair of 4.times.4 optical
switching matrices 21 and 22 for routing working traffic and
redundant protection traffic between first and second client
network elements (NE's) 23 and 24, and the rest of the optical ring
10. OCCS 20 also has a client interface 25 for transporting the
working traffic and the protection traffic between switching
matrices 21 and 22, and first and second client network elements 23
and 24. OCCS 20 further includes a ring interface 26 for
transporting the working traffic and the protection traffic between
the switching matrices 21 and 22 and the optical ring 10.
Turning now to FIG. 3, it can be seen that each client network
element has an electrical bridge 30 and a protection switch 31. The
electrical bridge 30 adds working traffic and protection traffic to
the client interface 25 via transmitters 32 and 33. The client
interface 25 then transports the added working traffic and
protection traffic to the pair of switching matrices 21 and 22.
During normal operation, the protection switch 31 selects the
working traffic as an incoming signal and the signal is received
through receiver 34. This signal is dropped from switching matrix
21. While the circuitry shown here is relatively simple, more
complex designs can be used to achieve the same objective.
Returning to FIG. 2, the matrix structure will now be described. A
pair of 4.times.4 switching matrices includes a first matrix 21 and
a second matrix 22. Generally, each matrix adds and drops traffic
to and from the optical ring 10. Adding is the process of routing a
signal transmitted from a client network element to the optical
ring 10, whereas dropping involves the process of routing a signal
from the optical ring 10 to a client network element. The client
network element retrieves the signal from either receiver 34 or 35
(FIG. 3) depending on the position of protection switch 31.
Specifically, the first matrix 21 adds working traffic from the
second client network element 24 to the optical ring 10. As an
example, it can be seen that the signal travels along the path 120,
121, 122, and 123 before reaching working span 100 of the optical
ring 10. The first matrix 21 also adds protection traffic from the
first client network element 23 to the optical ring 10. The first
matrix 21 drops the working traffic from the optical ring 10 to the
first client network element 23, and drops protection traffic from
the optical ring 10 to the second client network element 24. A
logic table of this structure is shown in FIG. 26.
The second matrix 22 adds working traffic from the first client
network element 23 to the optical ring 10, and adds protection
traffic from the second client network element 24 to the optical
ring 10. The second matrix 22 drops working traffic from the
optical ring 10 to the second client network element 24, and drops
protection traffic from the optical ring 10 to the first client
network element 23. A logic table of this structure is shown in
FIG. 27. As will be discussed below, the use of 4.times.4 matrix
pairs in conjunction with the above distribution of traffic allows
for self-healing of single point failures with minimal optical
switching.
With reference to FIG. 4, single point failures can occur in a
number of different locations. For example, a failure can occur in
a working span 100 anywhere along the optical ring 10. In this
case, the protection switch 31 selects the protection traffic as an
incoming signal and the switching matrices 21 and 22 do not change.
Thus, the selection is done by client network elements 23 and 24
via the protection switch 31 located downstream from the two
receivers 34 and 35 (FIG. 3). This switching process therefore
restores the traffic connection between network elements (Node A
and Node B) on either side of the failure as shown in FIG. 4. FIG.
5 better illustrates the ability of the switching matrices 21 and
22 to maintain their switch positions during such a failure.
A single point failure can also occur in the ring interface 26 as
shown in FIG. 6. Each ring interface has a first port 27 and a
second port 28. Each port (27 and 28) has two multiplexers 91 for
multiplexing the working traffic and the protection traffic to and
from the switching matrices 21 and 22. Each port (27 and 28) also
has two demultiplexers 92 for demultiplexing the working traffic
and the protection traffic to the switching matrices 21 and 22. It
is important to note that there may be other equipment present,
such as optical amplifiers, attenuators, and connectors. More
importantly, all of these devices and assemblies may be subject to
failure. Thus, the ability to self-heal shown in FIG. 6 can also
apply to these types of failures. It can be appreciated that only
the protection switches 31 of the client network elements affected
by the failure need be thrown in the case of failure.
FIG. 7 shows how the protection traffic is chosen when a switch
matrix such as optical switch matrix 21 fails. Here, protection
traffic is received by the first client network element 23 and
transmitted by the second client network element 24. A similar
procedure is followed for failure of switch matrix 22. FIG. 8 shows
how the protection traffic is selected as an incoming and an
outgoing signal when the single point failure occurs in the client
interface 25. It will be appreciated that the client interface 25
has a first client span 51 and a second client span 52. The first
client span 51 carries the working traffic and the protection
traffic from the switching matrices 21 and 22 to the first client
network element 23, whereas the second client span 52 carries the
working traffic and the protection traffic from the switching
matrices 21 and 22 to the second client network element 24. In the
preferred embodiment, each span 100, 200 comprises two
unidirectional optical fibers, but a single bi-directional optical
fiber can be used with additional splitting components.
FIGS. 9-11 show the failure of a working span 100 that is not
adjacent to add drop nodes (Node A and Node B). It can be
appreciated that the through Nodes C and D have no client network
elements for that optical channel and therefore do not need to
perform any switching by either the matrices or the clients. This
is shown in FIG. 11. Here, while no switches need to be thrown in
the through nodes, the nearest network elements, second client
network element 24 of Node B and third client network element 41 of
Node A, must throw their respective electrical protection switches
31. This is shown for client network element 24 in FIG. 10. The
same self-healing mechanism found in FIGS. 9-11 would apply if
there was an internal equipment failure within a through node, such
as a multiplexer device 92 (see FIG. 12) or an optical switch
matrix failure (see FIG. 13).
The more complicated scenario to overcome is a cable cut as shown
in FIG. 14. In this situation, client network elements at adjacent
nodes cannot simply choose the protection traffic from the same
ports as in earlier examples, because that routing has also been
interrupted. As shown in FIG. 15, Node B must therefore route the
working traffic from first client network element 23 to the
available protection spans 200 through the port opposite of the
cable cut. The through Nodes C and D send these signals to Node A,
where Node A connects them with client network element 40 in a
similar fashion. This requires coordinated action among Nodes A, B,
C, and D. Signaling among the nodes coordinates this
reconfiguration action. One implementation of such signaling would
be via messages sent across an optical supervisory channel that is
terminated by each OCCS.
Note that the working traffic connecting client network element 24
and 41 is not interrupted by the above self-healing procedure. The
protection traffic between client network elements 24 and client
network element 41, however, has been lost in order to use it to
reroute the optical channels between client network elements 23 and
40. The rearranged connections within Node B are shown in FIG. 15.
In FIG. 15, the protection traffic for second client network
element 24 is in an open connection state. The switching matrices
21 and 22 should be structured as to allow for this to occur.
Another option for FIG. 15 is for switching matrices 21 and 22 to
disconnect the protection add and drop to first client network
element 23. This would be consistent with an OCCS node that treats
the protection traffic as "extra traffic," in the sense used by
SONET/Synchronous Digital Hierarchy (SDH) shared protection rings.
If the through Nodes C an D have already been provisioned to
through-connect the appropriate protection traffic, then no
switching action is necessary. This is illustrated in FIG. 16.
Thus, returning to FIG. 15, when the single point failure occurs as
an adjacent cable cut, the first matrix 21 adds the working traffic
from the second client network element 24 to the optical ring 10.
The first matrix 21 also drops the protection traffic from the
optical ring 10 to the first client network element 23 as working
traffic. The second matrix 22 adds the working traffic from the
first client network element 23 to the optical ring 10 as
protection traffic, and drops the working traffic from the optical
ring 10 to the second client network element.
Another scenario to consider is a cable cut that does not occur
adjacent to either of the add drop nodes. Two types of switching
philosophies could be chosen. The first philosophy is to presume
that the nodes adjacent to the cable cut perform a loopback switch.
This self-healing mechanism is shown in FIG. 17. In this example, a
cable cut has occurred between Nodes C and D. This affects the
working traffic traveling between client network element 41 and 24.
The self-healing occurs by looping the affected working traffic
away from the failure via the protection spans 200, and eventually
placing the affected traffic back into working capacity. In this
example, the optical channel from client network element 24 to
client network element 41 takes a routing of Node B to Node C back
to Node B, then Node A, Node D, then back to Node A. Nodes not
adjacent to the failure, must therefore through-connect their
protection traffic. This is shown for Node B in FIG. 18.
One consequence of using this philosophy is that the network
elements originally provisioned to use their protection traffic
lose that ability. A ranking of failures is therefore necessary for
choosing which signal failure has priority when another failure
occurs. Such a ranking could be developed from that used for SONET
bi-directional line switched rings. The types of failures present
on the ring must also be signaled among all the nodes. An
implementation of this signaling could use the optical supervisory
channel presumed to be present between all the nodes. A means for
communicating a failure on the link between a client network
element and an OCCS is also needed, if such a failure is to be
considered in the overall switching priority.
In the present example illustrated in FIG. 17, Nodes C and D are
adjacent to the failure, so they take all the working traffic and
place it on the protection fibers away from the failure. The
switching action for Node D in FIG. 17 is shown in greater detail
in FIG. 19.
Thus, when the single point failure occurs as a non-adjacent cable
cut, nodes adjacent to the failure reverse the working traffic with
the protection traffic. Returning to FIG. 18, at Node B the first
matrix 21 adds the working traffic 100 from the second client
network element 24 to the optical ring 10 and passes the protection
traffic 200 through. The first matrix 21 also drops the working
traffic from the optical ring 10 to the first client network
element 23. The second matrix 22 adds the working traffic from the
first client network element 23 to the optical ring 10 and passes
the protection traffic through. The second matrix 22 also drops the
working traffic from the optical ring to the second client network
element 24.
Another philosophy is to presume that optical switching occurs
whenever the working traffic is added and dropped. This is commonly
termed "non-adjacent node switching." This self-healing mechanism
is shown in FIG. 20.
In this example, a cable cut has occurred between Nodes C and D.
This failure affects the working traffic traveling between client
network elements 24 and 41. It will be appreciated that in FIG. 17,
the optical channels between client network elements 24 and 41
travel twice through Nodes A and B. A simplification occurs if
Nodes A and B directly connect the working traffic to the
protection spans 200 that are opposite of the direction of the
failure. Here, the optical channel from client network element 24
to client network element 41 now takes a routing of Node B to Node
A on the protection span 200. This is more clearly shown for Node B
in FIG. 21. Another option for FIG. 21 is for switching matrices 21
and 22 to disconnect the protection add and drop to client network
element 24, for the reasons discussed with regard to FIG. 15.
Again, a consequence of using this philosophy is that the network
elements originally provisioned to use protection traffic loose
this capacity. As mentioned for the adjacent node switching
scenario, a ranking of failures is necessary to choose which signal
failure has priority when another failure occurs. The types of
failures present on the ring must also be signaled among all the
nodes.
An advantage of non-adjacent node switching over adjacent node
switching is that the longest restoration route can be no more than
the number of ring spans minus one. This is the same as the longest
possible working route, so no special engineering is needed for the
longest restoration route. For adjacent node switching, the longest
restoration route could be as large as twice the number of ring
spans minus three. The through nodes (Nodes C and D), are therefore
not obliged to take any switching action, even if they are adjacent
to the failure. This is shown for Node D in FIG. 22.
Thus, when a single point failure occurs as a non-adjacent cable
cut, the through nodes do not change. Returning to FIG. 21, at Node
B the first matrix 21 adds the working traffic from the second
client network element 24 to the optical ring 10 as protection
traffic. The first matrix 21 also drops the working traffic from
the optical ring 10 to the first client network element 23, and
drops the protection traffic from the optical ring 10 to the second
client network element 24. The second matrix 22 adds the working
traffic from the first client network element 23 to the optical
ring 10. The second matrix 22 further adds the protection traffic
from the second client network element 24 to the optical ring 10,
and drops the protection traffic from the optical ring 10 to the
second client network element 24 as working traffic.
Other embodiments of a bidirectional optical ring 10 in accordance
with the present invention are as follows. FIG. 23 shows a second
embodiment. In this configuration, each client network element uses
two different wavelengths for working traffic and protection
traffic, respectively. Therefore, for each network element, four
4.times.4 switches are needed. The plurality of switching matrices
includes a pair of first matrices 70 and a pair of second matrices
80. The pair of first matrices 70 routes the working traffic
between the plurality of clients and the optical ring 10 at a first
wavelength .lambda..sub.j. The pair of second matrices 80 route the
protection traffic between the plurality of clients and the optical
ring 10 at a second wavelength .lambda..sub.k.
Turning now to FIG. 24, a third embodiment is shown. In the third
embodiment, the working and protection transmitters use one
wavelength for each added client signal, and the working and
protection receivers use another wavelength for each dropped client
signal. Thus, once again four 4.times.4 switches are required to
connect a client network element. The plurality of switching
matrices includes a pair of first matrices 71 and a pair of second
matrices 81. The pair of first matrices 71 add the working traffic
and the protection traffic from the plurality of client network
elements to the optical ring 10 at a first wavelength
.lambda..sub.j. The pair of second matrices 81 drop the working
traffic and the protection traffic from the optical ring 10 to the
plurality of client network elements at a second wavelength
.lambda..sub.k.
A fourth embodiment is shown in FIG. 25. This configuration assigns
one wavelength to the working transmitters and protection
receivers, and another wavelength to working receivers and
protection transmitters. It can be seen in FIG. 25 that connecting
a client network element requires only two switches as in the
preferred configuration of FIG. 2. Unlike the preferred embodiment,
however, where the two switches are at the same wavelength, the two
switches in the fourth embodiment are at different wavelengths.
Thus, the plurality of switching matrices includes a pair of first
matrices 72 and a pair of second matrices 82. The pair of first
matrices 72 adds the working traffic from the plurality of clients
to the optical ring 10, and drops the protection traffic from the
optical ring 10 to the plurality of client network elements. The
pair of second matrices 82 adds the protection traffic from the
plurality of client network elements to the optical ring 10, and
drops the working traffic from the optical ring 10 to the plurality
of client network elements.
A single point failure in a bidirectional optical ring 10 can
therefore be self-healed by carrying working traffic and redundant
protection traffic between a plurality of cross-connect systems,
detecting the failure in the system, and rerouting the working
traffic and the protection traffic. Each OCCS 20 routes the working
traffic and the protection traffic through a plurality of 4.times.4
optical switching matrices to a client, and each client network
element selects the working traffic as an incoming signal under
normal operations.
Those skilled in the art can now appreciate from the foregoing
description that the broad teachings of the present invention can
be implemented in a variety of forms. Therefore, while this
invention has been described in connection with particular examples
thereof, the true scope of the invention should not be so limited
since other modifications will become apparent to the skilled
practitioner upon a study of the drawings, specification, and
following claims.
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